Apparatus and method integrating an electro-osmotic pump and microchannel assembly into a die package

ABSTRACT

A die package and a method and apparatus for integrating an electro-osmotic pump and a microchannel cooling assembly into a die package.

TECHNICAL FIELD

Various embodiments disclosed herein relate to the field of electronicpackage fabrication, and more specifically to a method and apparatusintegrating an electro-osmotic pump and a microchannel assembly into adie package.

BACKGROUND INFORMATION

Bare electronic chips typically need to be packaged in a package thatprovides an electric circuit between each electrical connection of thechip and an external connector such as a pin or a ball extending fromthe package to external circuitry such as a printed circuit board. Thecircuitry on the chip, particularly a very fast chip such as amicroprocessor, generates a considerable amount of heat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of a portion of anelectro-osmotic pump 100.

FIG. 2 is a graph 200 of current flow used for one embodiment of EO pump100.

FIG. 3A is a side cross-section schematic view of an electronics chip300A in process of fabricating an attached electro-osmotic (EO) pumpcooling system.

FIG. 3B is a side cross-section schematic view of a chip 300B inprocess.

FIG. 3C is a side cross-section schematic view of a chip 300C further inprocess.

FIG. 3D is a side cross-section schematic view of a chip 300D further inprocess.

FIG. 3E is a side cross-section schematic view of a chip 300E further inprocess.

FIG. 3F is a side cross-section schematic view of a chip 300F further inprocess.

FIG. 3G is a side cross-section schematic view of a chip 300G further inprocess.

FIG. 3H is a side cross-section schematic view of a chip 300H further inprocess.

FIG. 3I is a side cross-section schematic view of a chip 300I further inprocess.

FIG. 3J is a side cross-section schematic view of a chip 300J further inprocess.

FIG. 4A is a side cross-section schematic view of a chip 300A in processof fabricating a different attached electro-osmotic (EO) pump coolingsystem than is shown in FIGS. 3A-3J.

FIG. 4B is a side cross-section schematic view of a chip 300B further inprocess.

FIG. 4C is a side cross-section schematic view of a chip 300C further inprocess.

FIG. 4D is a side cross-section schematic view of a chip 400D further inprocess.

FIG. 4E is a side cross-section schematic view of a chip 400E further inprocess.

FIG. 4F is a side cross-section schematic view of a chip 400F further inprocess.

FIG. 4G is a side cross-section schematic view of a chip 400G further inprocess.

FIG. 4H is a side cross-section schematic view of a chip 400H further inprocess.

FIG. 4I is a side cross-section schematic view of a chip 400I further inprocess.

FIG. 4J is a side cross-section schematic view of a chip 400J further inprocess.

FIG. 4K is a side cross-section schematic view of a chip 400K further inprocess.

FIG. 5 is an exploded perspective view of an electronics part 500 inprocess.

FIG. 6 is an exploded perspective view of an electronics part 600 inprocess.

FIG. 7 is an exploded perspective view of an electronics part 700 inprocess.

FIG. 8 is a schematic view of an electronics part 800 having an EO pump.

FIG. 9 is a schematic view of an electronics part 900 having an EO pump.

FIG. 10 is a side cross-section schematic view of a chip 1000 having anEO pump.

FIG. 11 is a perspective schematic view of a system 1100 having a chip1120 having an EO pump.

FIG. 12 is a perspective schematic view of a package 1200 having an EOpump.

DETAILED DESCRIPTION

In the following detailed description of various embodiments, referenceis made to the accompanying drawings that form a part hereof, and inwhich are shown by way of illustration, some specific embodiments inwhich the subject matter may be practiced. It is understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

The leading digit(s) of reference numbers appearing in the Figuresgenerally corresponds to the Figure number in which that component isfirst introduced, such that the same reference number is used throughoutto refer to an identical component which appears in multiple Figures.The same reference number or label may refer to signals and connections,and the actual meaning will be clear from its use in the context of thedescription.

Terminology

The terms chip, die, integrated circuit, monolithic device,semiconductor device, and microelectronic device, are usedinterchangeably in this description.

The terms metal line, trace, wire, conductor, signal path and signalingmedium are all related. The related terms listed above, are generallyinterchangeable, and appear in order from specific to general. In thisfield, metal lines are sometimes referred to as traces, wires, lines,interconnect or simply metal. Metal lines, generally copper (Cu) or analloy of Cu and another metal such as nickel (Ni), aluminum (Al),titanium (Ti), molybdenum (Mo), or stacked layers of different metals,alloys or other combinations, are conductors that provide signal pathsfor coupling or interconnecting, electrical circuitry. Conductors otherthan metal are available in microelectronic devices. Materials such asdoped polysilicon, doped single-crystal silicon (often referred tosimply as diffusion, regardless of whether such doping is achieved bythermal diffusion or ion implantation), titanium (Ti), molybdenum (Mo),and refractory metal silicides are examples of other conductors.

In this description, the term metal applies both to substantially puresingle metallic elements and to alloys or combinations of two or moreelements, at least one of which is a metallic element.

The terms substrate or core generally refer to the physical structure orlayer that is the basic workpiece that is transformed by various processoperations into the desired microelectronic configuration. Substratesmay include conducting material (such as copper or aluminum), insulatingmaterial (such as sapphire, ceramic, or plastic), semiconductingmaterials (such as silicon), non-semiconducting materials, orcombinations of semiconducting and non-semiconducting materials. In someembodiments, substrates include layered structures, such as a core sheetor piece of material (such as iron-nickel alloy) chosen for itscoefficient of thermal expansion (CTE) that more closely matches the CTEof an adjacent structure such as a silicon processor chip. In someembodiments, such a substrate core is laminated to a sheet of materialchosen for electrical and/or thermal conductivity (such as a copper oraluminum alloy), which in turn is covered with a layer of plastic chosenfor electrical insulation, stability, and embossing characteristics. Insome embodiments, the plastic layer has wiring traces that carry signalsand electrical power horizontally, and vias that carry signals andelectrical power vertically between layers of traces.

The term vertical is defined to mean substantially perpendicular to themajor surface of a substrate. Height or depth refers to a distance in adirection perpendicular to the major surface of a substrate.

FIG. 1 is a perspective schematic view of a portion of anelectro-osmotic pump 100 according to some embodiments. Not shown is acover plate (for example, a planar structure that is attached in contactwith the top of edge walls 111 and channel walls 112), and the inlet andoutlet pipes, channels, or tubing that provide inlet fluid 98 andreceive outlet fluid 99. Substrate 110 has recesses formed in it whichform enclosed fluid channels once the cover plate (not shown) isattached. Substrate 110 can be made of plastic, glass, silicon, ceramic,or other suitable material. In some embodiments, substrate 110 is anelectronics chip, with the active electronics layer facing down, and therecesses etched in the back of the bulk layer. Inlet plenum 128 receivesthe inlet fluid (for example, water or other suitable fluid). Aplurality of relatively narrow channels 114 connect and allow transportof the fluid between inlet plenum 128 and outlet plenum 129. Anelectrode 116 is located towards the inlet-plenum end of most or allchannels 114 (for example, along the floor or ceiling of inlet plenum128), and another electrode 117 is located towards the outlet-plenum endof most or all channels 114 (for example, along the floor or ceiling ofoutlet plenum 129). In some embodiments, the inlet plenum 128 and theoutlet plenum are each tapered for space efficiency; since each pumpchannel draws a little fluid, the inlet plenum 128 can be made narrowertowards the next channel, and the outlet plenum is made wider after eachpump channel. In some embodiments, a plurality of rows of pump channelsand their respective electrodes are plumbed in series to obtain greaterflow and/or pressure. In some embodiments, voltage is applied betweenelectrode 116 and electrode 117, and one or more ionized species locatedin the electrical double layer moves from one electrode to the other,and thus causes a certain amount of fluid flow through channels 114 (theelectrical double layer is a region of molecular dimension at theboundary of two substances across which an electrical field exists. Thesubstances typically each contain electrically charged particles, suchas electrons, ions, or molecules with a separation of electricalcharges, e.g., polar molecules). In some embodiments, the channels havea cross-section that is quite small, for example, on the order of onemicron wide by ten microns long. In various embodiments the depth of thechannel may be anywhere from one micron to several hundred microns.

FIG. 2 is a graph 200 of current flow used for some embodiments ofelectro-osmotic pump 100. In some embodiments, for example using wateras the fluid, a DC current flow will soon cause bubbles of oxygen at oneelectrode and hydrogen at the other electrode. These bubbles, onceformed, can end up blocking the channels 114 and stopping or interferingwith the flow of fluid. To prevent this problem, some embodiments use analternating current, in order to neutralize bubble formation by having anet average of zero current. For example, a longer duration,lower-current positive pulse 211 establishes fluid flow, alternatingwith a shorter duration, higher-current negative pulse 210 thatneutralizes the ionized species to prevent bubble formation. In someembodiments, the relative proportion of the magnitude of positive andnegative current is inversely proportional to the duration of thepulses, such that there is a net average zero current flow averaged overa large period of time. In some embodiments, the absolute duration ofthe positive and negative pulse is varied in an experiment to determinean optimum ratio to obtain good fluid-flow rates and to avoid bubblesthat block flow.

In other embodiments, alternate channels are provided to collect thebubbles (for example, hydrogen and oxygen), to remix them and tochemically recombine them (for example, in the presence of a catalyst)to form water.

FIGS. 3A-3J show cross-sections of a chip after various process stepsused to form an integrated EO pump and microchannel cooling system forthe electronics of the chip. In some embodiments, the integrated EO pumpand microchannel cooling system is self contained on the chip package,and is used primarily to even out the heat distribution and eliminatehot-spots of concentrated heat. In other embodiments, external fluidconnections are provided, wherein the fluid is plumbed to an externalheat sink or heat-dissipation plate to be cooled and then returned tothe chip. In some embodiments, a single-phase, all liquid system isused. In other embodiments, a two-phase, liquid-gas system is used,wherein the pump moves liquid coolant from the heat sink to the hotspot, where it undergoes a phase change to a gas, which then moves tothe heat sink and is cooled to a liquid again.

FIG. 3A is a side cross-section schematic view of an embodiment of anelectronics chip 300A at one stage in a process of fabricating anattached electro-osmotic (EO) pump cooling system. The bulk portion 310is shown at the top, and the active region 311 is shown at the bottom.Active region 311 is, in some embodiments, a silicon-on-insulatorelectronics circuit, supporting functions such as a microprocessor,memory, bridge, controller, and/or communications.

FIG. 3B is a side cross-section schematic view of an electronics chip300B in some embodiments, after a temporary “handle” wafer 313 isattached to the active region 311 face, for example, using a layer ofsuitable glue 312. In some embodiments, handle wafer 313 is a polishedsilicon wafer used for its flatness and matched coefficient of thermalexpansion (CTE) to the wafer of interest (layers 311 and 310). In otherwords, after transistor and interconnect fabrication is complete, butbefore the bumping process commences (for external electricalconnections such as solder balls), the front-side of a wafer thatcontains the active silicon is attached using a glue to a silicon handlewafer.

FIG. 3C is a side cross-section schematic view of an electronics chip300C further in process after a polishing operation. At this point inthe process, much of the back of bulk layer 310 has been removed (forexample, by chemical-mechanical polishing), thus thinning the chip 305to a thin bulk layer 310′ and an active layer 311. This very thin waferlayer would be too fragile to handle or process alone, which is whyhandle wafer 313 was attached using glue 312.

FIG. 3D is a side cross-section schematic view of an electronics chip300D further in process. At this point in the process, a plurality ofholes 314 has been formed (for example, by etching throughphotolithographically defined openings).

FIG. 3E is a side cross-section schematic view of an electronics chip300E further in process. At this point in the process, a suitableelectrical conductor is deposited to fill or substantially fill vias314. In some embodiments, a layer 315 of metal (e.g., Cu or Al) isdeposited (e.g., using electro-deposition, sputter, or other suitabletechniques) in such a way that the vias are filled with the metal 316.

FIG. 3F is a side cross-section schematic view of an electronics chip300F further in process, in some embodiments. There are more than onepossible variation for this step. In some embodiments, the existingdeposited metal 315 (see FIG. 3E) is patterned and etched to form theresulting pump electrodes 317, as shown in FIG. 3G. In some embodiments,this variation is used when the electrode 317 and via layer metal 316are identical materials. In other embodiments, using polish and/oretch-back techniques, the top metal 315 is removed from the back of thewafer leaving metal 316 only in the vias, as shown in FIG. 3F. A secondlayer of metal that has different composition than the via metal 316 isdeposited, patterned and etched to form the electrodes 317 over thevias, resulting in the configuration of FIG. 3G.

FIG. 3G is a side cross-section schematic view of an electronics chip300G further in process. At this point in the process, the electrodes317 have been patterned and etched. In some embodiments, the metal ofelectrode 317 is the same as the metal of the via 316, while, in otherembodiments, a different type or composition of metal is used. In someembodiments, a thin layer of silicon oxide is deposited next, to form agood bond to later structures.

FIG. 3H is a side cross-section schematic view of an electronics chip300H further in process. At this point in the process, in someembodiments, oxide layer 318 has been deposited to improve the bond tosilicon (in some embodiments) channel wafer 320. Wafer 320 has alreadybeen processed to form pump channels 321, and cooling microchannels 322.Electrodes 317 provide electrical power for the pumps, which circulatethe cooling fluid through the microchannels 322 across the back of theelectronics chip (layers 310′ and 311), and then through, for example, aheat-dissipating plate or finned heat sink remote from the chip. Inother embodiments, the pump channels 321 and/or cooling channels 322 areinstead etched into the back of the thinned bulk layer 310′, and wafer320 merely forms an enclosure for the channels, for example, a flatcover plate.

FIG. 3I is a side cross-section schematic view of an electronics chip300I further in process. At this point in the process, the channel wafer320 has been attached (by standard wafer-bonding techniques such asanodic bonding, direct bonding or eutectic bonding) to the back face ofthinned bulk layer 310′, and the handle wafer 313 and glue layer 312have been removed (for example, by applying heat, etching, and/orsolvent). In some embodiments, the wafer is diced before removing thehandle layer 313.

FIG. 3J is a side cross-section schematic view of an electronics chip300J further in process, for some embodiments. At this point in theprocess, the chip has been bumped (for example, by adding solder balls330 that provide connections for electrical power to the EO pumps 333,and solder balls 331 that provide power and signal connections to theelectrical circuit of active layer 311. In this way, electrical powerfor the chip's circuitry in active layer 311 on the front of the chipand for the EO pumps 333 on the back of the chip (relative to the activelayer) are all brought in at the exposed face of active layer 311.

Thus, in these embodiments shown in FIGS. 3A-3J, the pump channels andconduits 321, as well as the cooling microchannels or conduits 322 areall formed in a single layer 320 (or in the back of layer 310′). This isparticularly useful in situations where there is sufficient lateral areato form sufficient EO pumps to be connected in parallel and/or series,as well as area for the cooling microchannels in order to obtain enoughfluid flow and cooling area to provide the desired cooling. The singlelayer also saves cost, manufacturing time, and complexity, as comparedto having these functions in separately made parts or layers. In someembodiments, the pumps and/or the microchannels are not simultaneouslyintegrated on the die with the electronics circuit. In some suchembodiments the pumps are made on a different piece of silicon and areassembled either within the same package as the electronics circuit andmicrochannels, or are connected to, but completely external to, thepackage having the microchannels.

FIGS. 4A-4K show cross-sections of a chip after various process stepsused to form an integrated EO pump and microchannel cooling system forthe electronics of the chip. This system provides a different structurefor an attached electro-osmotic (EO) pump cooling system than is shownin FIGS. 3A-3J.

FIG. 4A is a side cross-section schematic view of an electronics chip300A as described above for FIG. 3A. FIG. 4B is a side cross-sectionschematic view of an electronics chip 300B as described above for FIG.3B. FIG. 4C is a side cross-section schematic view of an electronicschip 300C as described above for FIG. 3C.

FIG. 4D is a side cross-section schematic view of an electronics chip400D further in process. As described above for FIG. 3D, a plurality ofvias 314 have been formed (e.g., by etching using a photolithographicmask) through the thinned bulk layer 310′ and the active layer 311 inorder to provide electrical connections from the front of the activelayer (i.e., the face adjoining glue layer 312) to the back of thethinned bulk layer where the EO pumps will be formed.

FIG. 4E is a side cross-section schematic view of an electronics chip400E further in process. At this point in the process, a metal layer hasbeen deposited in order to fill vias 314 with metal conductors 316, andthe surface metal (such as layer 315 of FIG. 3E) has been removed, asdescribed above for FIG. 3F.

FIG. 4F is a side cross-section schematic view of an electronics chip400F further in process. A wafer 414 (some embodiments use a siliconwafer 414 to better match CTE of the base silicon wafer (layers 311 and310′), wafer 414 having a plurality of grooves or microchannels 422etched in its surface is bonded (e.g., by anodic bonding or othersuitable wafer bonding techniques) to the surface of thinned bulk layer310′. The microchannels 422 provide the paths for circulating coolingfluid (such as water, in some embodiments).

FIG. 4G is a side cross-section schematic view of an electronics chip400G further in process. At this point in the process, the back of thewafer of microchannel layer 414 has been thinned by a suitable polishingtechnique as described above, to form thinned microchannel layer 414′,with top surface 415.

FIG. 4H is a side cross-section schematic view of an electronics chip400H further in process. At this point in the process, in someembodiments, vias have been etched through thinned microchannel layer414′ to connect to the tops of metal conductors 316, and these vias havebeen filled with metal to form conductors 416. In some embodiments, thetops of conductors 416 are flush with the exposed face of thinnedmicrochannel layer 414′ as shown in FIG. 4H (e.g., where a differentmetal will be deposited to form the electrodes 417—see FIG. 4I), whilein other embodiments, surface metal from the metal deposited to formconductors 416 is left to form the electrodes to drive the EO pumps inthe next layer (layer 420, described below).

FIG. 4I is a side cross-section schematic view of an electronics chip400I further in process. At this point in the process, the electrodes417 have been formed and patterned, and, in some embodiments, a layer ofsilicon oxide 418 or other suitable bonding interface material has beendeposited and planarized. Further, a plurality of through channels 419have been etched to provide paths to conduct fluid down into themicrochannels 422.

FIG. 4J is a side cross-section schematic view of an electronics chip400J further in process. At this point in the process, a wafer 420 (someembodiments use a silicon wafer 420 to better match CTE of theunderlying wafer layers 414, 311 and 310′) having a plurality of EO pumpgrooves or channels 421 and plenum openings 423 etched in its surface isbonded (e.g., by anodic bonding or other suitable wafer bondingtechniques) to the surface of thinned microchannel layer 414′. Thegrooves 421 and electrodes 417 form EO pumps 333 in the top layer 420that are in fluid communications with cooling microchannels 422 in theintermediate layer 414′. The plenum channels or openings 423 connectthrough opening 419 down into the microchannels 422 of thinned layer414′ to provide the paths for circulating cooling fluid (such as water,in some embodiments). Thus, in these embodiments shown in FIGS. 4A-4K,the pump channels and conduits are formed in layer 420, and the coolingmicrochannels or conduits are formed in a different layer 414′. This isparticularly useful in situations where more lateral area is needed toform EO pumps to be connected in parallel and/or series in order toobtain enough fluid flow to provide the desired cooling that is needed.

FIG. 4K is a side cross-section schematic view of an electronics chip400K further in process, wherein solder balls 330 for pump power andsolder balls 331 for chip power and signals have been attached.

FIG. 5 is an exploded perspective view of an electronics part 500,before attachment of the tubing needed for external plumbing. Part 500is similar to part 300J of FIG. 3J, but wherein inlet plenum 328, pumpchannels 321, and outlet plenum 329 also function as distributingcooling fluid across the back side of thinned bulk layer 310′ and activelayer 311. Part 500 is also similar to part 100 of FIG. 1, but whereinthe pump electrodes are formed on the cover layer (i.e., thinned chip305), and the electrical connections 316, 330 are formed through theactive layer 311. In some embodiments, part 500 when assembledrepresents the entire packaged electronics chip 305, just beforeattaching fluid-connection tubing to the side of inlet port plenum 328,and to the side of outlet port plenum 329. In other embodiments, part500 represents a small portion of a laterally much larger part havingfurther cooling channels and/or pump portions that are fabricated in thesame plane as inlet plenum 328, pump channels 321, and outlet plenum329, but laterally extending to the desired size.

FIG. 6 is an exploded perspective view of an electronics chip 600 inprocess, before attachment of the tubing needed for external plumbing.Part 600 is similar to part 400K of FIG. 4K, but wherein inlet plenum628 (holding inlet fluid 97) and pump channels 622 (of pump 421) areshown in pump layer 420. Intralayer via 419 conducts fluid 98 from pumpoutlet plenum 423 to the inlet plenum 627 of cooling layer 414′, wherethe fluid passes through microchannels 422 to outlet plenum 629, thuscooling active layer 311 by conduction through thinned bulk layer 310′.In some embodiments, an oxide bonding layer is provided between layer420 and layer 414′, and/or between layer 414′ and 310′. Power to thepump is provided through solder balls 330, and conductors 316 and 416 toelectrodes 417 of EO pump 421. Signal and power connections to circuitry601 are provided by solder balls 331. In some embodiments, part 600represents the entire electronics chip 315, just before attachingfluid-connection tubing to the side of inlet port plenum 328, and to theside of outlet port plenum 329. In other embodiments, part 500represents a small portion of a laterally much larger part havingfurther cooling channels and/or pump portions that are fabricated in thesame plane as inlet plenum 328, pump channels 321, and outlet plenum329, but laterally extending to the desired size, as shown in FIG. 3J,for example. The serially connected pumps in the figure areschematically shown for clarity, without attempting to show proportion.When the pumps are too close, there is typically a big power loss. Thus,in some embodiments, EO pumps in series are placed far apart, or onopposite sides of the chip or chip plenum.

FIG. 7 is an exploded perspective view of an electronics chip 700 inprocess. In this embodiment, an inlet plenum 728 receives inlet fluid 98and distributes the fluid to pump channels 321. Power to the pumpelectrodes 317 comes through conductors 316 (formed through active layer311 and thinned bulk layer 310′) and solder balls 330. The outlet fluidthen comes to outlet plenum 729 (sometimes a plurality of microchannels322 (e.g., formed on the inner surface of layer 720, or on the back ofchip 315) are also used to control the flow of the fluid across the backof chip 315). In some embodiments, a further row of pump channels (notshown) is placed at the outlet of the microchannels or centralreservoir. In some embodiments, two or more rows of pump channels andelectrodes are plumbed in series (see FIG. 9) with the pumps placedrelatively far apart in place of the single row of pump channels shown.The outlet fluid then exits through the near opening. In someembodiments, suitable tubing for connection to an externalheat-dissipation fluid circuit is attached to inlet opening 798 andoutlet opening 799. In some embodiments, chip 315 extends to the lateraledges of channel layer 720 to seal against edge walls 711, while inother embodiments, another structure at the outer edges of chip 315forms the outer-edge seal.

FIG. 8 is a schematic view of an electronics chip 800 having an EO pump801. Pump driver circuit 840 provides electrical power (e.g., such asshown in FIG. 2, or other suitable power) to electrodes 817, thusdrawing fluid through tubing 888, inlet plenum 898, pump channels 821,outlet plenum 899, tubing 889, and heat-dissipation plate or heatsink850, where the heat of the fluid is transferred to the ambientenvironment, and the cooled fluid is again circulated, starting attubing 888. In this embodiment, an electronics chip or circuit 815 is incontact with the fluid in the vicinity of the EO pump 801, which has aplurality of parallel channels.

FIG. 9 is a schematic view of an electronics chip 900 having an EO pumpthat includes pumps 821A and 821B plumbed in series. Pump driver circuit840′ provides electrical power (e.g., such as shown in FIG. 2, or othersuitable power) to respective electrodes 817, thus drawing fluid throughtubing 888, pump 821A and then through cooling plenum 880 which isagainst the chip or circuitry 815, then through tubing 889, through pump821B, and heat-dissipation plate or heatsink 850, where the heat of thefluid is transferred to the ambient environment, and the cooled fluid isagain circulated, starting at tubing 888. In this embodiment, anelectronics chip or circuit 815 is in contact with the fluid somewhatremote (e.g., an a separate stacked layer, or at a lateral distance)from the EO pump 801, which has a plurality of parallel channels, andtwo pumps in series to obtain greater flow and/or pressure.

FIG. 10 is a side cross-section schematic view of an electronics chip1000 having an EO pump 801. An inlet tubing 1010 and outlet tubing 1010are attached (e.g., using epoxy 1012). The rest of the referencenumerals and corresponding structures are described above.

FIG. 11 is a perspective schematic view of an electronics system 1100 ofsome embodiments (for example, a laptop computer or cell phone or otherdevice) having a chip 1120 having an EO pump. System 1100 optionallyincludes a top portion 1110 and a bottom portion 1116, a power supply1130 (such as a battery), an antenna 1140 (such as for a wireless LAN orcellular communications) a display 1111, one or more input/outputdevices such as a keyboard 1112, a diskette 1113, and/or a DVD/CDROM1114 or other devices. One or more electronics chips 1120 (each havingan EO pump) is connected (for example, by tubing 1122) to a cold plate(e.g., a sheet of copper or aluminum used to dissipate heat and cool thecirculating fluid). The one or more electronics chips 1120 can be any ofthe chip/pump structures described herein, such as, for example, 100 ofFIG. 1, 300J of FIG. 3J, 400K of FIG. 4K, 500 of FIG. 5, 600 of FIG. 6,700 of FIG. 7, or 1200 of FIG. 12.

FIG. 12 is a perspective schematic view of some embodiments, having anelectronics package 1200 including an EO pump. In these embodiments, anelectronics chip 1210 is enclosed within a case 1220 that includes a topcover 1221 and a bottom cover 1223 (for example, both made from one ormore layers of silicon wafers, ceramic, or other suitable material).Solder-ball connections 330 (for the EO pump) and 331 (for the chip1210) are formed on the external surface of bottom cover 1223. A wellwithin case 1220 holds chip 1210, and also forms the inlet plenum 1228and outlet plenum 1229. In some embodiments, the well is etched to asuitable depth into the bottom cover. In some embodiments, a pluralityof via holes are formed through the bottom cover, and filled with metalsuch as copper or aluminum to form electrical contacts between insidecomponents, including the EO pump, and the outside environment. Aplurality of parallel channels 321, and the appropriate electrodes formthe EO pump, for example, as discussed for FIG. 7. Inlet and outlettubing 1010 are attached to the case using, for example, epoxy 1012, oranodic bonding, direct bonding or eutectic bonding, or other suitableattachment means. Electrical connections are made between solder balls331 and chip 1210 through the bottom cover by, for example, metal viasas described above.

In some embodiments, prototype micropumps with 0.15 cm³ packages producea maximum flow rate of 170 μL min⁻¹ and a maximum pressure of 10 kPaoperating at 400 V. These specifications approach the requirements forsingle-phase forced-convective cooling of some embodiments of small IChot spots. In some embodiments, the micropumps operate on less than 200mW and, having no moving structural elements, offer inherent reliabilityadvantages.

Continued performance improvements for many integrated circuit devicesmay require new cooling solutions incorporating liquid or two-phaseforced convection. Miniature pumps that generate electro-osmotic flowusing sintered glass frits have been developed to provide two-phaseconvective cooling for high-power-density integrated circuits (Yao, S.,et al., Porous Glass Electroosmotic Pumps. Submitted to Journal ofColloid and Interface Science.). These pumps generate over oneatmosphere of pressure at 100 V and can pump liquids at flow rates ashigh as 33 mL min⁻¹.

Electro-osmotic frit pumps produce high pressures and flow rates in highsurface-to-volume-ratio structures with sub-micron pores.High-aspect-ratio structures suitable for electro-osmotic pumping canalso be made using micromachining techniques (Chen, C.-H. and J. G.Santiago, A Planar Electroosmotic Micropump. Journal ofMicroelectromechanical Systems, 2002. 11(6): p. 672-683.). In themicrofabricated pump shown in FIG. 1 (not to scale), narrow slots etchedin a silicon substrate form a high surface-to-volume-ratio structure forgenerating relatively high pressure and flow rate electro-osmotic flow.In some embodiments, a layer of silicon nitride coats the siliconsubstrate, providing reliable insulation for operation at up toapproximately 500 V. In some embodiments, micropumps based on thisdesign produced flow rates on the order of 10 μL min⁻¹ and pressures onthe order of 10 kPa (Laser, D. J., et al. High-Frequency Actuation withSilicon Electroosmotic Micropumps. 2002 Solid State Sensors andActuators and Microsystems Workshop, 2002, Hilton Head, S.C.).

Since these micropumps have no moving structural elements and arefabricated in a CMOS-compatible process, they are suitable for some ICthermal management applications. One such application is reducing thetemperature of small, high-power-density regions of microchips throughsingle-phase forced-convective cooling. Systems-on-a-chip (SoC) andhigh-performance ICs that contain a mix of high- and low-power devicesare prone to developing hot spots during operation. Even with chip-scaleheat sinking adequate for the chip's overall power dissipation, thethermal resistance associated with solid-state conduction to the heatsink may be too great to avoid excessive hot-spot temperatures. This isparticularly true for chips with multiple active layers in a 3-Dconfiguration [Banerjee, K., et al., 3-D ICs: A Novel Chip Design forImproving Deep-Submicrometer Interconnect Performance andSystems-on-Chip Integration. Proceedings of the IEEE, 2001. 89(5): p.602-633.]. A single-phase forced-convection cooling system like the oneillustrated in FIG. 3J or 4K is a possible solution. The systemincorporates an integrated electro-osmotic micropump, avoiding the needfor fluidic connections to the chip. Similar systems incorporatingarrays of feedback-controlled silicon electro-osmotic micropumps couldprovide on-demand forced convective cooling of spatially- andtemporally-varying hot spots.

Zhang et al. showed that a flow rate of 100 μL min⁻¹ is sufficient forcooling some hot spots [Zhang, L., et al., Measurements and modeling oftwo-phase flow in microchannels with nearly constant heat flux boundaryconditions. Journal of Microelectromechanical Systems, 2002. 11(1): p.12-19.]. To estimate the micropump performance requirements for hot spotcooling generally, one can use a simple model of a single-phasemicrochannel heat sink [Murakami, Y. and B. B. Mikic, ParametricOptimization of Multichanneled Heat Sinks for VLSI Cooling. IEEETransactions on Components and Packaging Technologies, 2001. 24(1): p.2-9.]. This model assumes a very small thermal resistance in the solid(Biot number much less than one). It is estimated that the calculatedflow rate required for single-phase forced-convective cooling of a 1mm×1 mm hot spot with a local microchannel heat sink designed tominimize required pumping power is about 0.31 mL/min/W. Thecorresponding pressure drop (across microchannel heat sink) is about0.07 kPa/W. These estimates were made using the properties of water at30° C. and a channel-to-chip cross-sectional area ratio of 0.25. Fromthis analysis, one can conclude that, for an allowed fluid temperaturerise of 70° C., forced convective cooling of a 2 W hot spot requires aflow rate of approximately 620 μL min⁻¹. The corresponding pressure dropacross the microchannel heat sink is approximately 0.14 kPa. Pressurelosses in the rest of the system are estimated at 1-10 kPa. Siliconelectro-osmotic micropumps for hot spot cooling, therefore, mustgenerate flow rates between one and two orders of magnitude greater thanearly prototypes while maintaining pressure performance.

The design variables for electro-osmotic micropumps include pumpgeometry, surface treatment, and the chemistry of the workingelectrolyte. For an electro-osmotic pump with deep, narrow slot-shapedfeatures (i.e., a slot geometry with slot height b>>2a (=total slotwidth) and pump slot length l>>2a) and uniform and constant surface andfluid properties, the flow rate Q that results from applying a uniformaxial electrical field E_(x) is [Hunter, R. J., Zeta Potential inColloid Science. 1981, San Diego: Academic Press, Inc.; Burgreen, D. andF. R. Nakache, Electrokinetic Flow in Ultrafine Capillary Slits. J.Phys. Chemistry, 1964. 68(5): p. 1084-1091.]:Q=A{−μ/eofE/x[1−G(a/λ _(D))]−φ₂ p ₁}  (1)where p₁ is the pressure increase in the pump and A is the total flowcross-sectional area (A=2abn, where 2a and b are the slot width andheight, respectively, cross-sectional dimensions defined above, and n isthe number of slots). The electro-osmotic mobility μ_(eo) and theparameter φ₁ are$\mu_{eo} = {{\frac{ɛ\quad\varsigma}{\mu}\quad{and}\quad\phi_{i}} = \frac{a^{2}}{3\quad\mu\quad l}}$

-   -   where μ and ε are the viscosity and permittivity, respectively,        of the fluid and ζ is the zeta potential, defined as the        potential drop across the diffuse ion region of the electrical        double layer. The function G ranges from 0 to 1, depending on        the ratio of the slot half-width, a, and the Debye length,        λ_(D), which is the characteristic thickness of the electric        double layer in the region of the liquid/solid interface. In        some embodiments, micropumps are operated with weak buffer        solutions for which λ_(D) is of order 100 nm or smaller. These        micropumps have slot half-height a≧1 μm, so finite double layer        effects are negligible and G<<1. Therefore, flow rate is        expected to scale linearly with A and l⁻¹ for a given voltage        applied across the pumping region.

Viscous losses in the manifolds of silicon electro-osmotic micropumpscan be significant. Approximating flow in the manifolds of our designwith a parallel-plate flow model, the pressure increase from the inletto the outlet of the pump p₂ is$p_{2} = {{{- \frac{\mu_{eo}}{\phi_{1}}}{E_{x}\left\lbrack {1 - {G\left( \frac{a}{\lambda_{D}} \right)}} \right\rbrack}} - {\left( {\frac{1}{A\quad\phi_{1}} + \frac{1}{\phi_{2}}} \right)Q}}$

-   -   where the parameter φ₂ accounts for pressure drops in the        manifolds in terms of the effective manifold cross-sectional        dimensions a_(m) and b_(m) and its length l_(m):        $\phi_{2} = {\frac{2}{3}{\frac{a_{m}^{3}b_{m}}{\mu\quad l_{m}}.}}$

Electro-osmotic micropumps have been fabricated on 4″ silicon wafers ina two-mask process. The slots and manifolds are defined in 7 μm thickphotoresist (SPR-220-7) and etched by deep reactive ion enhancedetching. Inlet and outlet ports are then etched from the back side ofthe wafer. After etching, a layer of near-stoichiometric silicon nitrideis deposited at low pressure. A glass cover is then anodically bonded tothe nitride-coated wafer to seal the slots and manifolds. The wafer isthen diced into individual pumps, platinum wires are inserted into themanifolds through channels running to the sides of the dies, and 0.5 cmlong glass tubes are epoxied on to the dies to serve as interconnects.In some embodiments, thin-film platinum electrode processes are used forelectroosmotic pumps.

In some embodiments, the micropumps each have 500 slots spaced at 20 μmintervals, forming a pumping region 1 cm wide. The volume occupied bythe pumping regions is less than 1 mm³. In some embodiments, for ease offixturing (e.g., attaching fluidic interconnects), the micropumps arefabricated on 1.2 cm×1.3 cm dies. In some embodiments, the siliconnitride passivation layer is 400 μm thick. Slot depth b is approximately70 μm. In various embodiments, micropumps have slot lengths l of 100 μm,200 μm, or 400 μm, or other suitable lengths. In some embodiments,micropumps are fabricated with an oxide coating on top of the nitridelayer. The oxide coating is applied in the high-aspect-ratio slots byperforming a short LPCVD polysilicon deposition followed by wetoxidation of the polysilicon layer in its entirety. The slot height 2aof oxide-coated micropumps is approximately 2.8 μm; the slot height ofthe nitride-only micropumps is approximately 2.2 μm, in someembodiments.

In some embodiments, the silicon electro-osmotic micropumps are usedwith borate buffer solutions (Na₂B₄O₇, pH=9.2) with concentrations(based on Na⁺) of 0.2 mM and 0.4 mM. The measured conductivities ofthese solutions were 15 μS cm⁻¹ and 28 μS cm⁻¹, respectively. In someembodiments, the micropumps are used at operating voltages of 200 V and400 V. In one test, only one of the 22 micropumps tested under theseconditions failed due to breakdown of the passivation layer andresultant short-circuiting through the silicon substrate. Flow rateunder minimal back pressure conditions was measured by tracking theposition of the flow front in an open capillary. Pressure vs. flow ratemeasurements were performed by measuring compression of a gas column ina closed capillary. The margin of error associated with theopen-capillary flow rate measurement technique is approximately 5%; themargin of error for the closed-capillary pressure-flow rate measurementtechnique is approximately 15%. Current was monitored during tests byobserving the voltage drop across a small reference resistor in serieswith the micropump. The margin of error associated with this measurementtechnique is approximately 15%. Some variation in micropump performancewas observed from day to day and over the course of repeated testingduring a particular day. The data reported here is from micropumps thathad been allowed to stand for at least three days between tests.

Pressure-flow rate results were repeatable within +/−30% for multipletests of the same micropump and for tests of different micropumps withthe same geometry and surface. Measured power consumption wasapproximately 150 mW at 400 V and 40 mW at 200 V. Thermodynamicefficiency is approximately 0.05%. Zeta potential, estimated from themaximum generated pressures using (1) above, was found to be between −20and −25 mV.

Micropumps with 100 μm, 200 μm, and 400 μm long pumping regions (in theflow direction) were tested under minimal-back-pressure conditions at200 V with 0.2 mM and 0.4 mM buffers. The electric field in the pumpingregion was estimated with a one-dimensional model to account forpotential drops in the manifolds. As expected, flow rate per unitapplied field is generally independent of pump length. No dependence ofperformance on buffer concentration was discernable for the two bufferconcentrations used. Micropumps with oxide-coated pumping surfacesconsistently produced higher Q_(max) than those with bare nitridepumping surfaces.

Current flow is expected to result from electromigration in themicropumps during operation. The electromigration current is predictedfrom the micropump geometry and the measured bulk buffer conductivity.

Relative to their size, the flow rate produced by the siliconelectro-osmotic micropumps exceeds that of many reciprocatingdisplacement micropumps that require more complex fabrication processes.Pressure generation is comparable to that of many reciprocatingdisplacement micropumps. Measured micropump performance was generallyconsistent with models for electro-osmotic flow. Some variation inmicropump performance for low buffer concentration experiments may bedue to unstable pH conditions. Also, at very low concentrations, ionicimpurities from surfaces and gases in contact with the buffer (e.g.,carbonic acid resulting from CO₂-water reactions) can have a significantimpact on buffer conductivity. At times, measurements of buffersconductivity several hours or days after preparation revealedsignificant deviation (+/−25%) from the nominal values. This wasparticularly the case for the 0.2 mM buffer. The micropumps were alsotested with buffers at concentrations below 0.2 mM, but conductivity(and performance) variations with these buffers were so great that thetests were discontinued. Operating at concentrations below 0.2 mM, whiledesirable from the standpoint of maximizing micropump efficiency, isimpractical. Operating at 200 V with 0.2 mM and 0.4 mM buffers, themicropumps consume less than 50 mW.

Silicon electro-osmotic micropumps for integrated circuit thermalmanagement applications have been fabricated and tested. Reducing thelength of the pumping region and coating the pumping surfaces withsilicon oxide has been shown to significantly improve micropumpperformance. Micropumps with 100 μm long pumping regions andoxide-coated pumping surfaces produce a maximum flow rate and pressureof 170 μL min⁻¹ and 10 kPa, respectively, at 400 V. This flow rate ismore than an order of magnitude higher than that produced by earlierprototypes.

In some embodiments, the cooling channels and the pump channels areformed in a layer of silicon, in order to better match the CTE of thesilicon electronics layer. In other embodiments, the cooling channelsand the pump channels are formed in a layer of glass, plastic, ceramic,or other suitable material.

In some embodiments, the package assembly is designed so that the fluidinlet and outlet ports occur from the edges of the silicon (or glass,etc.) package, rather than from the top or bottom face of the package.This can provide simplified internal and external plumbing. In someembodiments, reservoirs formed in the package that contain the coolantfluid are arranged such that they connect together forming a fluid paththat is substantially in a single plane (used, for example, to reducecost), or in a stack of parallel planes (used, for example to increasefluid flow) parallel to the electronics chip. Forming both the pumpchannels and the cooling channels in a single layer of silicon reducesthermal mismatch, cost and complexity. Sealing of the pump assembly intothe package helps ensure that coolant fluid does not leak between theinlet and outlet ports, or around electrical connections between theelectronics chip and the pump electrodes. Thinning the electronics chipallows easier fabrication of the vias that provide electricalconnections between the front of the electronics chip (where all theother electrical connections are made) and the back of that chip wherethe pump electrodes are located. Thinning also provides a lowerresistance to heat flow between the active electronics layer and thecooling fluid channels and reservoirs.

Some embodiments relate to an apparatus having an electronics chip 315having a substrate with a first face thereof having circuitry thereon,and an opposite second face, and one or more electro-osmotic pumps 333in a layer over the second face.

In some embodiments, the electro-osmotic pumps include capillary pumpchannels in a further layer over the second face of the electronicschip, as described for FIGS. 3A-3J.

In some embodiments, cooling channels are also formed in a further layerover the second face of the electronics chip in fluid communication withthe electro-osmotic pumps.

In some embodiments, external fluid connections to the pumps are made atlateral edges of the apparatus 1000, as described in FIG. 10.

In some embodiments, electrical power for the electro-osmotic pumps isconducted by electrical conductors formed through the electronics chip.

In some embodiments, cooling channels are formed in a further layer ofmaterial over the second face of the electronics chip, and theelectro-osmotic pumps are in fluid communication with the coolingchannels, as described for FIGS. 4A-4K.

In some embodiments, electrical power for the electro-osmotic pumps isconducted by electrical conductors formed through the electronics chipto the pumps. In some embodiments, the cooling channels are formed inthe same layer as the capillary pump channels. In some embodiments, thechip is silicon, and the electro-osmotic pumps are formed in a furtherlayer of silicon over the second face of the silicon chip in fluidcommunication with the cooling channels. In some embodiments, externalfluid connections are made at lateral edges of the electronics chip.

In some embodiments, electrical power for the electro-osmotic pumps isconducted by electrical conductors formed through the electronics chip.In some embodiments, the chip is made of silicon, and theelectro-osmotic pumps include capillary pump channels formed in thelayer of silicon over the second face of the chip.

In some embodiments, the chip includes circuitry for at least a portionof a processor, and the apparatus further includes a memory operativelycoupled to the processor, an input/output system, including a displayunit, operatively coupled to the processor, and a power supplyoperatively coupled to the processor.

In some embodiments, the chip includes circuitry for at least a portionof a telecommunications circuit, and the apparatus further includes anantenna operatively coupled to the telecommunications circuit, aninput/output system, including a display unit, operatively coupled tothe telecommunications circuit, and a power supply operatively coupledto the telecommunications circuit.

Other embodiments include a method for cooling an electronics chiphaving a substrate with a first face having circuitry thereon, and anopposite second face. The method includes pumping a cooling fluidthermally coupled to the second face with one or more electro-osmoticpumps positioned over the second face.

In some embodiments of the method, the electro-osmotic pumps includecapillary channels in a layer of material over the second face of theelectronics chip, and wherein the pumping includes electroosmoticallyflowing the cooling fluid in the capillary channels.

Some embodiments of the method further include flowing the cooling fluidthrough external fluid connections at lateral edges of the electronicschip and the layer containing the electro-osmotic pumps.

Some embodiments of the method further include conducting electricalpower for the electro-osmotic pumps by electrical conductors passingthrough the electronics chip.

Other embodiments include a method that includes providing anelectronics chip having a substrate with a first face having circuitrythereon, and an opposite second face, and providing at least one layerof material over the second face, one of the at least one layers formingat least one electro-osmotic pump.

Some embodiments of this method further include forming cooling channelsin one of the at least one layers of material over the second face ofthe electronics chip, the channels operatively coupled to one of the atleast one electro-osmotic pumps.

Some embodiments of this method further include attaching a handle layerto the first face of the electronics chip, and thinning the electronicschip by polishing and/or etching the second face of the electronicschip.

Some embodiments of this method further include forming electricalconductors through the electronics chip, for supplying electrical powerfor the electro-osmotic pumps.

In some embodiments, the chip is made of silicon, and the layer ofsilicon over the second face of the circuit die is attached to thesilicon chip.

Some embodiments of this method further include packaging theelectronics chip into a package, mounting the package onto a circuitboard having other circuitry, and coupling the packaged electronics chipto supply of fluid to the electro-osmotic pump.

Other embodiments include an apparatus that includes an electronicschip, and electro-osmotic pump for circulating cooling fluid throughcooling channels adjacent a face of the chip. In some embodiments, theelectro-osmotic pump and the cooling channel are in separate layers ofmaterial attached to the face of the chip. In some embodiments theelectro-osmotic pump and the cooling channel are in the same layer ofmaterial. In some embodiments the electro-osmotic pumping means and thecooling channel are in substantially the same plane.

The accompanying drawings that form a part hereof, show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment.

1. An apparatus comprising: an electronics chip having a substrate witha first face thereof having circuitry thereon, and an opposite secondface; and one or more electro-osmotic pumps in a layer over the secondface.
 2. The apparatus of claim 1, wherein the electro-osmotic pumpsinclude capillary pump channels in a further layer over the second faceof the electronics chip.
 3. The apparatus of claim 2, wherein coolingchannels are formed in a further layer over the second face of theelectronics chip in fluid communication with the electro-osmotic pumps.4. The apparatus of claim 3, wherein external fluid connections to thepumps are made at lateral edges of the apparatus.
 5. The apparatus ofclaim 1, wherein electrical power for the electro-osmotic pumps isconducted by electrical conductors formed through the electronics chip.6. The apparatus of claim 2, wherein cooling channels are formed in afurther layer of material over the second face of the electronics chip,and the electro-osmotic pumps are in fluid communication with thecooling channels.
 7. The apparatus of claim 6, wherein external fluidconnections to the pumps are made at lateral edges of the apparatus. 8.The apparatus of claim 6, wherein electrical power for theelectro-osmotic pumps is conducted by electrical conductors through theelectronics chip to the pumps.
 9. The apparatus of claim 1, wherein thecooling channels are formed in the same layer as the capillary pumpchannels.
 10. The apparatus of claim 1, wherein the electronics chip issilicon, cooling channels are formed in a layer of silicon over thesecond face of the electronics chip, and the electro-osmotic pumps areformed in a further layer of silicon over the second face of the siliconchip in fluid communication with the cooling channels.
 11. The apparatusof claim 10, wherein external fluid connections are made at lateraledges of the apparatus.
 12. The apparatus of claim 10, whereinelectrical power for the electro-osmotic pumps is conducted byelectrical conductors formed through the electronics chip.
 13. Theapparatus of claim 1, wherein the chip is made of silicon, and theelectro-osmotic pumps include capillary pump channels formed in a layerof silicon over the second face of the chip.
 14. The apparatus of claim1, wherein the chip includes circuitry for at least a portion of aprocessor, the apparatus further comprising: a memory operativelycoupled to the processor; an input/output system, including a displayunit, operatively coupled to the processor; and a power supplyoperatively coupled to the processor.
 15. The apparatus of claim 1,wherein the chip includes circuitry for at least a portion of atelecommunications circuit, the apparatus further comprising: an antennaoperatively coupled to the telecommunications circuit; an input/outputsystem, including a display unit, operatively coupled to thetelecommunications circuit; and a power supply operatively coupled tothe telecommunications circuit.
 16. A method for cooling an electronicschip on a substrate with a first face thereof having circuitry thereon,and an opposite second face, the method comprising: pumping a coolingfluid thermally coupled to the second face with one or moreelectro-osmotic pumps positioned over the second face.
 17. The method ofclaim 16, wherein the electro-osmotic pumps include capillary channelsin a layer of material over the second face of the electronics chip, andwherein the pumping includes electroosmotically flowing the coolingfluid in the capillary channels.
 18. The method of claim 16, furthercomprising: flowing the cooling fluid through external fluid connectionsat lateral edges of the electronics chip and the layer containing theelectro-osmotic pumps.
 19. The method of claim 16, further comprising:conducting electrical power for the electro-osmotic pumps throughelectrical conductors passing through the electronics chip.
 20. A methodcomprising: providing an electronics chip having a substrate with afirst face having circuitry thereon, and an opposite second face; andproviding at least one layer of material over the second face, one ofthe at least one layers forming at least one electro-osmotic pump. 21.The method of claim 20, further comprising: forming cooling channels inone of the at least one layers of material over the second face of theelectronics chip, the channels operatively coupled to one of the atleast one electro-osmotic pumps.
 22. The method of claim 21, furthercomprising: attaching a handle layer to the first face of theelectronics chip; and thinning the electronics chip by polishing and/oretching the second face of the electronics chip.
 23. The method of claim22, further comprising: forming electrical conductors through theelectronics chip, for supplying electrical power to the electro-osmoticpumps.
 24. The method of claim 23, wherein the chip is made of silicon,and the layer silicon over the second face of the circuit die isattached to the silicon chip.
 25. The method of claim 23, furthercomprising: packaging the electronics chip into a package; mounting thepackage onto a circuit board having other circuitry; and coupling thepackaged electronics chip to supply of fluid to the electro-osmoticpump.
 26. An apparatus comprising: an electronics chip; and anelectro-osmotic pump for circulating cooling fluid through coolingchannels adjacent a face of the chip.
 27. The apparatus of claim 26,wherein the electro-osmotic pump and the cooling channel are in separatelayers of material attached to the face of the chip.
 28. The apparatusof claim 27, wherein the electro-osmotic pump and the cooling channelare in the same layer of material.
 29. The apparatus of claim 28,wherein the electro-osmotic pumping means and the cooling channel are insubstantially the same plane.